1. Field of the Invention
The present invention relates generally to the field of magnetic disk drives, and more particularly to an apparatus for writing data to a magnetic disk.
2. Description of the Prior Art
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1 and 2, a magnetic disk data storage system 10 includes a sealed enclosure 12, a disk drive motor 14, and a magnetic disk, or media, 16 supported for rotation by a drive spindle 17 of motor 14. Also included are an actuator 18 and an arm 20 attached to an actuator spindle 21 of actuator 18. A suspension 22 is coupled at one end to the arm 20 and at another end to a read/write head 24. The suspension 22 and the read/write head 24 are commonly collectively referred to as a head gimbal assembly (HGA). The read/write head 24 typically includes an inductive write element and a magnetoresistive read element that are held in a very close proximity to the magnetic disk 16. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the read/write head 24 causing the read/write head to lift slightly off of the surface of the magnetic disk 16, or, as it is commonly termed in the art, to “fly” above the magnetic disk 16. Data bits can be written or read along a magnetic “track” of the magnetic disk 16 as the magnetic disk 16 rotates past the read/write head 24. The actuator 18 translates the read/write head 24 from one magnetic track to another by pivoting the arm 20 and the suspension 22 in an arc indicated by arrows P. The design of magnetic disk data storage system 10 is well known to those skilled in the art.
FIG. 3 shows a cross-sectional view of a read/write head. The read/write head includes a write element 30 for writing data bits to a magnetic disk and a read element 32 for reading the data bits. The read element 32 includes a first shield 34, a second shield 36, a read insulation layer 38 disposed between the first shield 34 and the second shield 36, and a read sensor 40 disposed within the read insulation layer 38 and exposed at an air bearing surface (ABS). The read sensor 40 can be, for example, a magnetoresistive sensor such as a giant magnetoresistive (GMR) device or an anisotropic magnetoresistive (AMR) device.
The write element 30 includes a yoke 42 and one or more layers of electrically conductive coils 44 wound around the yoke 42. The yoke 42 includes a lower pole 46 connected to an upper pole 48 by a back gap 50 at a back gap end. The lower and upper poles 46, 48 oppose each other across a write gap 52 at an air bearing end. In some designs, often referred to as “merged head” designs, second shield 36 and lower pole 46 are the same layer. In other designs, such as the one shown in FIG. 3, a thin insulating layer 54 separates the second shield 36 from the lower pole 46. In operation, an electric current is passed through the coils 44 to induce a magnetic field in the yoke 42. As the induced magnetic field bridges the write gap 52, lines of magnetic flux arch outward across the ABS and intersect the nearby magnetic disk (not shown). Bits of data are written where the lines of magnetic flux intersect the magnetic disk.
In a stitched pole design for a write element 30, the upper pole 48 includes a yoke portion 56 coupled to a pole tip portion 58. The yoke portion 56, sometimes referred to as a third pole or “P3,” extends between the back gap 50 and the pole tip portion 58, sometimes referred to as a second pole or “P2.” The yoke portion 56 typically does not extend all of the way to the ABS. Instead, an insulating material (not shown) fills the space between the ABS and an opposing face 60 of the yoke portion 56. The opposing face 60 of the yoke portion 56 is recessed from the ABS by a distance, P3R. Recessing the opposing face 60 from the ABS helps to prevent magnetic flux from escaping from the opposing face 60 and bridging the distance to the magnetic disk which can corrupt existing data bits. Since the amount of magnetic flux reaching the magnetic disk from the opposing face 60 decreases as a function of P3R, designers seeks to make P3R at least large enough that the amount of magnetic flux reaching the magnetic disk from the opposing face 60 is less than some acceptable threshold.
FIG. 4 shows a plan view of the yoke portion 56 and the pole tip portion 58 of the write element 30 of FIG. 3 as viewed from above. The pole tip portion 58 includes a narrow nose segment 62 to restrict the magnetic flux (shown as a set of arrows) to a narrow area at the ABS. The pole tip portion 58 widens behind the nose segment 62 into a broad segment 64 that connects with the yoke portion 56 over a stitched area 66 through which magnetic flux can pass between the yoke portion 56 and the pole tip portion 58. The stitched area 66 is preferably maximized to maximize the amount of magnetic flux available at the nose segment 62 to write bits to the magnetic disk. The stitched area 66 is maximized by designing pole tip portion 58 such that the broad segment 64 reaches its full width at, or in front of, P3R.
It can also be seen from FIG. 4 that magnetic flux can also leak from portions 68 of the broad segment 64 around the nose segment 62 that are closer to the ABS than P3R. This magnetic flux leakage creates an undesirable effect commonly known as “side writing.” In essence, side writing is the tendency of the write element to influence the magnetic disk on either side of the track to which it is writing. Like magnetic flux leakage from the opposing face 60, described above, side writing is deleterious because it can corrupt adjacent tracks. To alleviate problems of side writing, successive tracks must be written further apart, thus lowering the data density of the magnetic disk.
Accordingly, what is needed is a design for a pole tip portion of an upper pole that can allow more magnetic flux to reach the ABS while at the same time reducing magnetic flux leakage from around the nose segment.